Thermococcus, Methanococcus and Methanobacterium exemplify:

1. Archaebacteria that contain protein homologous to eukaryotic core histones
2. Archaebacteria that lack any histones resembling those found in eukaryotes but whose DNA is negatively supercoiled
3. Bacteria whose DNA is relaxed or positively supercoiled but which have a cytoskeleton as well as mitochondria
4. Bacteria that contain a cytoskeleton and ribosomes

Thermococcus, Methanococcus and Methanobacterium exemplify archaebacteria that contain protein homologous to eukaryotic core histones.